As Conventional gas-barrier polymers, polymers which have a highly hydrogen bonding group with high hydrophilicity, such as poly(meth) acrylic acid and polyvinyl alcohol, have been used. Films of these polymers show very high gas barrier properties against oxygen or the like under dry conditions. Under highly humid conditions, however, the gas barrier properties against oxygen or the like are drastically lowered and the films are poor in resistance to moisture or hot water because of the hydrophilicity.
To solve these problems, WO 03/091317 (Patent Document 1) discloses that a polycarboxylic acid polymer layer and a polyvalent metal compound-containing layer are formed adjacent to each other on a support film, and a polyvalent metal salt of polycarboxylic acid polymer is formed by interlayer reaction. The gas-barrier films thus produced are shown to have high oxygen barrier properties even under high humidity.
However, the gas-barrier films of Patent Document 1 reduce gas barrier properties or are clouded when exposed to cold water.
In regard to gas-barrier films that do not reduce gas barrier properties or are not clouded when exposed to cold water, the present applicant has filed patent applications directed to coating liquids containing a polycarboxylic acid polymer partially neutralized with a polyvalent metal (and an alkali metal) in which part of the carboxyl groups of the polycarboxylic acid polymer are neutralized with a polyvalent metal (and an alkali metal), and to gas-barrier films obtained from the coating liquids (Japanese Patent Application Nos. 2006-121602 and 2006-121604).
However, the coating liquids substantially disclosed in the above patent applications are often inferior in coating properties and require improvements.
Patent Document 1: WO 03/091317